I'd like this as well. Would be helpful for videos and stuff.
Exactly. I am also going to revive the idea of using Filipe's faces to get the effect as well.

It would have to be server sided somehow to override the avatar changing delay. Would work like this:
x=Keybind
Pressing x will have your mouth move in a talking animation.
Pressing x will have your mouth open into an O.
Pressing x will make you blink.
Etc.